Electric heater



Feb. 3, 1942. c HJELMGREN. 2,271,977

ELECTRIC HEATER Filed Oct; 10, 1959 2 Sheets-Sheet 1 Inv enter-1 CharlesI. H jelm gr en,

H IS Attornqg Feb 3, 9 c. l. HJELMGREN 2,271,977

ELECTRIC HEATER Filed Oc t. 10, 19:59

2 Sheets-Sheet 2 Inventor: Charles I, H 'elm ren,

b ax? His Attohhe g.

Patented Feb. 3, 1942 rmc'r'arc HEATER Charles I. Hielmgren,Chicago,lll., assignor to Edison'General Electric Appliance Company,Inc.," a corporation of New York Application October v10, 1939, SerialNo. 298,819

6 Claims. (01. 219-31) This invention relates to electric heaters, moreparticularly to electric heaters of the hotplate type, such as used withelectric ranges, and it has for its object the provision of an, improveddevice of this character. '1'

This invention has particula application to electric hotplates havingsheath, wire heating elements arranged in the form of flat loops orcoils. Certain sheath wire heating elements have a resistance conductorhoused in a metallic sheath and embedded in and supported in with thisinvention; Fig. 2 is a sectional view taken on the line 2-2 of Fig. 1and looking in the direction of the arrows; Fig. 3 is an enlargedfragmentary sectional view taken through the line 3+3 of Fig. l andlooking in the direction of the arrows; Fig. 4 is a sectional view takenthrough the line 4-4 of Fig. 1 and looking in the direction of thearrows; Figs. 5 and 6 are elespaced relation with the sheath by acompacted layer of heat conducting, electrically insulating material,such as powdered magnesium oxide. One heating unit of this type isdescribed in the U. S. patent to C. C. Abbott,'No. 1,367,341, datedFebruary 1, 1921.

In a particular electric range hotplate employing a sheath wire elementof this type, the

turns of the element are supported by metallic strips formed into agrid-like spider, the turns being rigidly secured to the strips. Theends of the strips are mounted in a supporting ring which functions tohold the spider and the heating element mounted on it in the top openingof the range.

As there is considerable expansion and contraction in the turns of theheating element as its temperature is elevated and reduced, and as theyare secured to the strips, strains are set up in the strips which mayresult in buckling of the heating element so that it is no longer flat,or in bending of the outer ends of the strips, whereby the outer turnsof the element are loosened.

This invention contemplates an improved electric heater whereinth'e'holding strips for the various convolutions of the heatingelements, instead of being rigidly fixed to each other, are relativelymovable, thereby relieving the strains inthe strips and heating elementsduring expansion and contraction of the elements.

This invention further contemplates an im-- proved connection betweenthe strips which provides for the relative movement between them, andalso which has considerable mechanical strength so that the strips willsupport the turns of the heating element in their normal plane even whenheavily loaded by a;cooking appliance.

For amore complete understanding of this invention, reference should behad to the accompanying drawings in which Fig. 1 is a plan view of anelectric hotplate having a pair oi heating elements, and provided withholding means for ments used to make the electric'hotplate shown inFigs. 1, 2, 3 and 4; Fig. '7 is a plan view of an .electric hotplate ofmodified form arranged in accordance with this invention; Fig. 8 is asectional view taken through the line 8-8 of Fig. 7 and looking in thedirection of the arrows; and Figs. 9, 10, 11 and 12 illustrate certainelements used in making the hotplate of Figs. '7 and 8, Figs. 9, 11 and12 being perspective views of the elements of these figures, and Fig. 10being a development of the element shown in Fig. 9. Referring moreparticularly to Figs. 1-6 inclusive, this invention has been shown asapplied to an electric range hotplate of the type described and claimedin the copending application of John C. Sharp, Serial No. 311,147, filedDecember 2'7, 1939, and assigned to the same assignee as this invention.As there described, this hotplate comprises a pair of heating elementsIll and H which are of the sheathed type such as described and claimedin the above-mentioned Abbott Patent No. 1,367,341. Each of theseelements comprises a coiled resistance conductor I! mounted in ametallic sheath l3 and embedded in and supported in spaced relation withreference to the sheath by a highly compacted layer It of heatconducting and electrically insulating material; any suitableelectrically insulating material-may be used, such as powdered magnetheheating elements arranged in accordance 5B sium oxide. The, oxide may becompacted inany suitable manner as by reducing the sheath. The sheathmay be reduced in any suitable way as by rolling, swaging or drawing.The heating element In, as shown, is formed into a partial circle,

while the element H is formed into a spiral positioned inside of theelement In. The terminal ends Illa and Ila of the two elements areadjacent each other at one side of the hotplate and are secured to aterminal shield lib.

In accordance with the invention, the heating elements liland H aresupported upon a suitable spider-like grid l5 which-in turn is supportedin a supporting member l6 which is adapted to, fit within the opening I!of the top plate [8 of an electric range. The supporting member l6, asshown, is provided with an annular surface l9 that rests directly uponthe top plate l8. De-

pending from the inner edge of the surface I! is a circular wall 20.This wall 20 is utilized to support the grid l5.

The grid I is formed of three diverging striplike members 23, 24 and 25arranged generally radially within the circular supporting wall 20.These strips are positioned vertically within the ring, as shown inFigs. 1 and 2, and preferably they will be aranged at angles ofsubstantially 120 to each other.

The two legs 23 and 24 span the terminal ends of the heater elements.and they are provided with a socket 25 which is rigidly secured to them,and which is adapted to receive the inner end of the leg 25 with a closesliding fit.

While the legs 23 and 24 and the socket 25 may be formed as separatemembers and secured together in any suitable manner, I prefer to formthem from a single piece of metal. For this purpose, a blank of metal 21as shown in Fig. 5 is used. The blank is folded along the two dottedlines designated 25 and 29 to bring the two legs 23 and 24 intosubstantially parallel arrangement. This will also bring the walls 25aand 25a on opposite sides of the lines 25 and 23 into substantiallyparallel arrangement. The area 35 between the lines 23 and 28 definesthe bottom wall of the socket 25, while the walls 28a and23a define theside walls of the socket. The top of the socket is closed by two tabs 3|and 32 which are folded over in the manner indicated in Fig. 2. Afterthe socket 25 has thus been formed the legs 23 and 24 are bent outwardlyalong the lines 33 and 34 to the required angle between them, as shownin Fig. 1.

The outer ends of the two legs 23 and 24 are provided with tongues 35and 35,'and the outer end of the leg 25 is provided with a similartongue 3'! which are adapted to be received in openings 33 provided forthem in the vertical wall 20. As shown. the openings 33 are verticallypositioned in the wall and these openings at the bottom merge intoelongated horizontal openings 39. The tongues 35, 35 and 31 aresupported within the openings 38 by means of sections 45 of the wall 25pressed inwardly from the plane of the wall under the elongated openings35, as clearly shown in Figs. 1, 2 and 3.

It will be observed, therefore, that the grid I5 is defined by two legstogether, and by a third leg 25 having its inner end received in asocket 25 rigidly secured to the legs 23 and 24. A sufficient length ofthe end portion of the leg 25 is inserted in the socket 25 to provide arigid, mechanically strong grid at the center which prevents any saggingof the g id.

The turns of the heating elements Ill and II, as shown, are mounted inrecesses or indentations 4| provided in the upper edges of the arms 23,24 and 25. The upper edges of the opposite side walls of as to hold theunits rigidly to the strips, as shown in Fig. 4. It will be understoodthat by reason of the sliding connection between the strip 25 and thestrips 23 and 24, it can move relatively to these strips to provide forexpansion and contraction of the heating elements I5 and II as they areheated and cooled. Inasmuch as only one loop of the heating element lllies between the strips 23 and 24 on the terminal side of the hotplatevery little stress is set up at this side of the plate, and it-is notnecessary toprovide for relative movement between the strips 23 and 24.

23 and 24 rigidly secured the recesses are peened over so are a numberof loops of the two elements it and H lying within the 240 space betweenthe strips 23 and 24 on the opposite side of the hotplate, and,therefore, substantially all expansion and contraction takes place here.The strip 25 is free to move relative to the strips 23 and 24 andprevents the setting up of strains in the heating elements, and therebyobviates permanent distortion of the heating elements and breakage ofthe supporting strips.

As shown, a reflector 4ia is provided which is mounted on a flange 4ibformed on the wall 20.

In the form of my invention shown in Figs. 7-12 inclusive the hotplateis provided with four supporting strips 42, 43, 44 and 45 positionedsubstantially at right angles to each other and extending radially fromthe center of the hotplate outwardly to the supporting member 45. Thesupporting member 45 is provided with an annular surface 451: from thedges of which two circular walls 45b and 450 depend. The wall 45!)rests upon a flange 45d formed in the range top so as to support thehotplate. The two heating elements 43 and 45 are formed into spiralsnested one within the other, as shown. These heating elements arerigidly mounted in the strips 42--45 inclusive in the same way as in thefirst form by means of indentations formed in the upper edges of thestrips.

Moreover, the strips are provided at their outer ends with tongues 5|which are supported in apertures 52 provided in the wall 45c in the samemanner that the outer ends of the strips 23, 24 and 25 are supported bythe member IS.

The strips 42-45, however, of this form are secured together in asomewhat different fashion than in the first form disclosed, but aresecured for relative movement and also are secured to prevent sagging atthe center of the unit, as are the strips-of the first form.

In the case of the hotplate shown in Figs. 7-12, a suitable interlockingmember 53 is provided to mechanically interlock the ends of the strips-43-45 together. The member 53 is provided with walls defining anelongated socket 54 into which the inner ends 42a and 44a of the strips42 and 44 are received. The ends 42a and 44a are received in overlappingrelation in the socket 54, as shown in Fig. 7, and preferably they willbe slightly oil'set, as shown in this figure and in Fig. 12, so that thebodies of the strips 42 and 44 will be in substantial alignment.

The side walls of the socket 54 are provided with cross-shaped openings55 and the inner ends 420 and 44a of the strips 42 and 44 are I providedwith elongated openings 55 which reg- However, as shown, there 7 isterwith the openings 55 and which preferably are somewhat longer than theseopenings. The openings 55 in the socket and theopenings 55 in the strips42 and 44 receive the inner ends 51 and 550i the strips 43 and 45,which, as shown in Figs. 7 and 8, are directed -through these openings.The two ends 51 and 58 of the strips 42 and 44 are arranged inoverlapped parallel relation, but are spaced somewhat from each other byend sections 59 on the two members arranged at right angles to the ends51 and 53 and directed towards each other, as clearly shown in Fig. 7.These angular extensions 55 terminate in tongues iii which are receivedin elongated apertures 6| provided for them in the strips.

The extreme end portions 51 and 53 of the strips 43 and 45 preferablywill have a lesser width than the in Fig. ii; that is, the portions ofthe ends of the strips which protrude from the opposite sides of thesocket will be reducedin width.

To reenforce and stabilize the inner end sections and 58 of the strips43 and 44, seats 62 and $3 are provided on opposite sides of the socket5% in spaced relation with reference to it, as clearly shown in Figs. '7and 9. These seats each having a relatively deep recess 64 in which therelatively wide inner portion 51a of one of the strips isreceivedbeforelt enters the openlugs 55 and 56 and with a relativelyshallow recess or seat 65 which receives the protruding end section 5?of the other strip.

The socket 54 and the seats 62 and 63 may be formed as separate memberssecured together in any suitable manner, but I prefer to form them froma single piece of material. They may be made from a single piece ofmaterial which is blanked out as shown in Fig. 10. This sheet ofmaterial is bent along the lines indicated 66 and @l to bring the twopieces of material 68 and 69 into substantially parallel relation. Theareas of the sections 68 and 69 define the side walls of the socket,while the area of the material between the lines 66 and 6'! defines thetop wall of the socket. The bottom wall is defined by tabs H and it!which are bent inwardly at right angles to the wall areas 68 and 69respectively along the lines ila and 12a, and are secured to tabs l3 and"M respectively which are bent outwardly at right angles to the wallsections 68 and 59, as shown in Fig. 9. The tabs El and 72 are securedto the tabs 13 and I l in any suitable manner, as by welding. The seats62 and 63 are defined by bending roughly triangular-shaped pieces l5 andi6 outwardly along dotted lines indicated ill and 18 so as to lie atright angles to the walls t8 and 69 respectively, as shown in Fig. 9.Then the end sections in which the seats 62 and 63 are included are bentupwardly along the dotted lines l9 and 80 to the positions shown in Fig.9. Preferably, the openings 55 and the slots \34 and 66 will be formedin the blank shown in Fig. 10 before it is formed into the supportingmember 53.

In this form of the invention, it will be observed that the two strips52 and 44 can move relatively to each other in the plane of the grid,the openings 56 being 'suillciently long to permit substantial relativemovement between these members without interferin with the ends of theother two strips 33 and 45 which pass through them. Likewise, the strips43 and 45 can move longitudinally in the plane of the grid, theelongated openings ti providing for a substantially longitudinalmovement of the tongues '30 which are received in them.

While I have shown particular embodiments of my invention, it will beunderstood, of course, that I do not wish to be limited there% sincemany modifications may be made, and I, therefore, contemplate by theappended claims to cover any such modifications as fall within the truespirit and scope of my invention.

What I claim as new and desire to secure by Letters Patent of the UnitedStates is:

1. An electricheater comprising a sheath wire heating element having athermally expansible and contractilole rigid sheath arranged into asubstantially ilat cell, a plurality of radially arranged divergingstrips upon which said coil is mounted having their inner ends adjacenteach other, means rigidly securing the turns of said coil to saidstrips, a supporting member for the outer ends of said strips, andconnection means between said inner ends including a part on the innerend of one of said strips interfitting with a complementary part securedto the inner ends of the remaining strips so as to provide for freesliding movement between said parts, and said interfitting parts haveinterengaged surfaces of sufficient area to support said strips andheating element at the center so as to prevent sagging of the strips,and also of the turns of said heating element from the plane of saidcoil.

2. An electric heater comprising a sheath wire heating element having ametallic sheath arranged into a substantially flat coil, a supportingmember for said coil having a continuous supporting wall with spacedapertures therein, means supporting said coil within said supportingmember including at least a pair of strips to which the turns of saidcoil are secured, said strips having their outer ends received in saidapertures and their inner ends adjacent each other, and means connectingsaid inner ends togather comprising an elongated socket connected to theinner end of one of said strips and in which the inner end of another isclosely fitted for free sliding movement so as to permit substantiallyfree expansion and contraction of said turns, the socket receiving asufiicient length of said inner end of the other of said strips toprevent sagging of the inner ends of said strips.

3. An electric heater comprising a sheath wire heating element having athermally expansible and contractible sheath arranged into asubstantially fiat coil, a supporting member for said coil having acontinuous supporting wall, a plur'ality of strips to which the turns ofsaid coil are secured diverging from each other at relatively wideangles and having their outer ends attached to said supporting wall, asocket rigidly attached to inner ends of certain of said strips andreceiving the inner end of another in free sliding engagement, thesocket receiving a sufilcient length of said end to prevent sagging ofthe inner ends of said strips.

4. An electric heater comprising a sheath wire heating element having ametallic sheath arranged into a substantially flat coil, a supportingmember for said coil having a continuous supporting wall, a plurality ofstrips to which the turns of said coil are secured diverging from eachother at relatively wide angles, the outer ends of said strips beingprovided with tongues which are fitted into apertures provided for themin said supporting wall, and a socket rigidly attached to the inner endsof certain of said strips and receiving the inner end of another in freesliding engagement, the socket receiving a sufiicient length of said endto prevent sagging of the inner ends of said strips.

5. An electric heater comprising a sheath wire heating element having athermally expansible and contractible sheath arranged into asubstantially flat coil, a supporting member for said coil, a stripfolded upon itself to'form a socket and two legs diverging from saidsocket at a relatively wide angle, a second strip having one endslidably received in said socket, means connecting the other end of saidsecond strip and the ends of said diverging legs to said supportingmember, and means securing the turns of said coil to said second stripand legs, the relative sliding movement between said second strip andsaid socket providing for the free expansion and contraction of saidturns.

6. An electric hotplate comprising a sheathed 4t set ew heating elementhaving an expansible and 3011- tractible sheath formed into a partialcircle, a second sheathed heating element having an expansible andcontractible sheath formed into a flat spiral positioned within thefirst, the two terminal ends of the two heaters being adjacent eachother at one side of the hotplate, a grid supporting said heatingelements having a pair of strips rigidly secured together and arrangedat a wide angle to each other and positioned to W

